Reproduction in Flowering Plants

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Reproduction in Flowering Plants
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Sexual Reproduction in Plants

• Flowers contain the sex organs of plants. They
  have four groups of organs carpels, stamens,
  petals, and sepals.

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Sexual Reproduction in Plants

• Carpels are female sex organs. A pistil is a
  structure composed of one or more carpels.
• The base of the pistil is the ovary, which
  contains one or more ovules.
• Each ovule contains a megasporangium.
• The stalk of the pistil is the style, and the end
  of the style is the stigma.

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Sexual Reproduction in Plants

• Stamens are male sex organs.
• Each stamen is composed of a filament bearing a
  two-lobed anther, which consists of four
  microsporangia fused together.
• Petals and sepals of many flowers are arranged in
  whorls (circles) around the carpels and stamens.
• All parts of the flower are borne on a stem tip,
  the receptacle.

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Sexual Reproduction in Plants

• The multicellular, diploid plant is called the
  sporophyte.
• In angiosperms (flowering plants), the diploid
  sporophyte generation is the larger and more
  conspicuous one.
• Cells contained in sporangia undergo meiosis to
  produce haploid spores.
• Mitosis produces the haploid plant (gametophyte)

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Sexual Reproduction in Plants

• Female gametophytes, the megagametophytes, are
  called embryo sacs and develop in megasporangia.
• Male gametophytes, the microgametophytes, are
  called pollen grains and develop in
  microsporangia.

Mature embryo sac of lily
Pollen grains of an eudicot
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Figure 39.1 Development of Gametophytes and
Nuclear Fusion (Part 1)
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Figure 39.1 Development of Gametophytes and
Nuclear Fusion (Part 2)
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Sexual Reproduction in Plants

• In angiosperms, the transfer of pollen from the
  anther to the stigma is called pollination.
• In some plants self-fertilization occurs by
  direct contact of anther and stigma before the
  flower bud opens.

Pollen grains adhere to sticky stigma.
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Sexual Reproduction in Plants

• The pollen of many species is carried from plant
  to plant by wind. These plants produce pollen
  grains in great numbers.
• Water carries pollen to some aquatic plants.
• Animals such as insects, birds, and bats carry
  pollen among the flowers of many plants.

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Sexual Reproduction in Plants

• Plants can cross-pollinate or self-pollinate.
• Many plants are self-incompatible their stigma
  rejects the pollen from their own flowers.
• The stigma can also reject pollen from other
  species. Pollen from the same species binds
  strongly to the stigma foreign pollen falls off.

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Sexual Reproduction in Plants

• After a pollen grain lands on the stigma of a
  compatible pistil, a pollen tube develops from
  the grain.
• The pollen tube traverses the style until it
  reaches an ovule.

Pollen tube germinated in vitro.
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Sexual Reproduction in Plants

• During transport through the pollen tube, the
  pollen grain cell undergoes one mitotic division
  to produce two haploid sperm cells.
• One sperm cell unites with the two polar nuclei,
  forming the 3n endosperm.
• The other sperm cell fuses with the egg cell,
  forming the diploid zygote.

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Sexual Reproduction in Plants

• After fertilization, the zygote divides and the
  two daughter cells have different fates.
• One daughter cell produces the embryo and the
  other produces a supporting structure.
• The embryo is called a Cotyledon an embryonic
  organ that stores and digests reserve materials
  (a seed leaf).

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Sexual Reproduction in Plants

• In some species the cotyledons absorb the
  nutrient reserves from the endosperm.
• The seed will lose as much as 95 percent of its
  water content.
• The embryo remains quiescent in this desiccated
  state until conditions are right for germination.

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Sexual Reproduction in Plants

• In flowering plants, the ovary wall together with
  its seeds develops into a fruit.
• Fruits serve to help seed dispersal.
• Winged fruit can be blown by the wind.
• Coconuts have spread from island to island by
  floating in the ocean.
• Some seeds hitch rides on animals.
• Fleshy, edible fruits may be eaten by birds and
  other animals and the seeds pass through the
  digestive tract.